This invention relates to optical device arrays for sensing or emitting energy and, more particularly, to such optical device arrays that are curved.
Many imaging sensor systems utilize an optical system to focus the infrared or visible-light energy of a scene onto a detector array. One widely used detector array is the focal plane array (FPA), in which an array of detector elements is positioned at the focal plane of the optical system. The infrared or visible-light energy focused onto the detector elements is converted to electrical signals. The electrical signals indicative of the image are viewed on a display or processed by a computer, as for example with pattern recognition techniques.
Existing imaging sensor systems with focal plane array detectors are widely used but have limitations in some applications. Illumination falling on the detector and resolution decrease with increasing deviation from the boresight axis of the detector. The imaging sensor systems have technically imposed size restrictions that limit their ability to be reduced in size. Consequently, the imaging sensor systems cannot be used for some tactical applications. Some of the same problems arise with light-emitter arrays such as diode or laser arrays.
There is a need for an improved approach to optical device array structures systems that will improve their optical performance and allow their sizes to be reduced. The present invention fulfills this need, and further provides related advantages.
The present invention provides an optical device array structure that is curved. In one embodiment, the present invention provides a curved imaging detector array structure that otherwise is structured similarly (but not identically) to a planar array of the FPA type. The curved imaging detector array structure utilizes the microelectronic component structures that are known for use in FPAs, such as monolithic and hybrid arrays, but modifies these structures to be suitable for use in a curved imaging detector array structure. The curved imaging detector array structure achieves improved optical performance with more uniform illumination and improved resolution at large off-axis angles, as compared with a conventional FPA. Additionally, the curved imaging detector array structure allows the imaging sensor system to be built more compactly than possible with a planar imaging detector array. In another embodiment, the present invention provides a curved optical emitter array structure in which the individual elements of the array lie on a curved emitter surface. The curved optical emitter array structure utilizes microelectronic component structures that are otherwise known, such as diodes or lasers, but modifies these structures to be suitable for use in the curved optical emitter array structure. It achieves the same advantages of compactness and better uniformity as does the imaging detector array.
In accordance with the invention, an integrated optical device array structure comprises a plurality of interconnected solid state microelectronic optical device elements associated together on a substrate structure. Each optical device element lies on a nonplanar optical array surface and comprises an opto-electronic device that interconverts an optical signal and an opto-electronic device electrical signal. Typically, each of the opto-electronic devices is substantially planar and lies in an opto-electronic device plane, and the opto-electronic device planes are piecewise tangential to the optical array surface. There may also be an electrical interface circuit that is in electrical communication with the opto-electronic device electrical signal. The opto-electronic device may be a light detector or a light emitter.
In accordance with a specific embodiment of the invention, an integrated imaging detector array structure comprises a plurality of interconnected solid state sensor elements associated together on a substrate. Each sensor element comprises a detector that converts energy incident upon the detector into a detector electrical signal. The detector is typically a semiconductor device. Each detector lies on a nonplanar optical array surface. The detectors and their detector surfaces are preferably each substantially planar in a respective detector plane, and the detector planes are piecewise tangential to the optical array surface.
In one design, each sensor element further includes a readout circuit that receives the detector electrical signal. The detector and the readout circuit may be a monolithic circuit or a hybridized circuit. In these cases, the readout circuit is preferably curved with the same curvature as the optical array surface.
The optical array surface may be singly curved, as in the case of a segment of a cylindrical surface, or doubly curved, as in the case of a segment of a spherical surface. The optical array surface may be regularly curved or complexly curved.
A method for preparing a curved integrated optical device array structure comprises the steps of providing a plurality of interconnected solid state microelectronic optical device elements associated together on a substrate structure, with each optical device element comprising an opto-electronic device that interconverts an optical signal and an opto-electronic device electrical signal. The plurality of optical devices is deformed into a deformed shape such that each opto-electronic device lies on a nonplanar optical array surface. The deformed optical device array structure may be affixed to a curved support to retain the deformed shape. In one embodiment, the method includes the steps, prior to the step of deforming, of providing an electrical interface circuit, and joining the plurality of optical devices to the electrical interface circuit. In an additional step, performed simultaneously with the step of deforming the plurality of optical devices, the electrical interface circuit is deformed into the same deformed shape as the plurality of optical devices.
The use of the curved imaging detector array structure, as distinct from the known focal plane array that is planar, results in the ability to reduce the size and improve the quality of the imaging sensor system. When a focal plane array is placed close to the focusing optics, the image quality is degraded at large off-axis angles in part because the focal plane of the imaging optics does not coincide with the plane of the focal plane array over all angles. The present approach allows the use of lenses in the optical system that produce a curved focal plane, and the curvature of the imaging detector array structure is matched to that curved focal plane. Similarly, a curved optical emitter array structure allows the construction of a smaller and optically more accurate light source or imaging light source.
Optical device array structures differ from other electronic devices and sensors in that their opto-electronic devices (that is, the element that receives or emits light) are pointed in a direction in space that is optimal for receiving (in the case of a detector) or emitting (in the case of an emitter) a light signal. The opto-electronic devices must be structured so that the directional pointing may be achieved with the requisite degrees of freedom, most generally three angular and three translational degrees of freedom. Unless care is taken to ensure that each opto-electronic device is not internally constrained against movement in the required degrees of freedom, the array of opto-electronic devices will distort when it is curved resulting in array defects such as wrinkles, folds, and ripples in the surface of the array. Such defects alter the local pointing direction of individual ones of the opto-electronic devices, and are therefore unacceptable in the present application. For many applications in other types of devices, such as non-directional sensors or electronic devices that do not involve directional pointing, such defects are not unacceptable unless they become so large as to cause a gross distortion and/or failure of the array. The individual opto-electronic devices of the present approach remain piecewise tangential to the optical array surface, and the array is not distorted.